"I'm carb loading" is a joke I often hear (and use!) when reaching for that frosty glass of beer. However deep down we all know this isn't the truth and while there are energy calories in alcohol (a whole 7 Kcal/g versus 9 Kcal/g in fat and 4 Kcal/g in carbohydrates), alcohol is pretty useless as a short-term energy source, in addition to the fact that it is devoid of any nutrients.
So, let's look at this simplified explanation of what happens when you drink a few beers:
More: Alcohol: The Benefits and Risks
Most of the alcohol in the beer heads into your bloodstream and is immediately treated as a toxin by your body. Where do toxins end up? In the liver!
The liver gets to work straight away metabolizing the alcohol using powerful enzymes, but there's only so much enzyme capacity in there, so any excess alcohol circulates your blood stream waiting for its time to come to be metabolized. In the meantime it plays havoc with your heart, brain, other tissues and organs (legs muscles go a bit wobbly, brain a bit more relaxed, reaction time not so cat like...sound familiar?).
More: Alcohol, Athletes and the Pressure to Drink
Glycogen Replenishment Halts
In addition to the alcohol consumed there's also a good dose of carbohydrates in beer. "No problem! That's my recovery fuel" I hear you say. Sadly—no, it doesn't work this way. Since the liver enzymes are working at full speed to rid your body of the alcohol toxins they aren't available to be used for normal energy metabolism functions and glucose conversion to glycogen grinds to a halt (glycogen being the stored form of glucose in your muscles).
In the same way that the body doesn't like a heap of alcohol to be swimming around in your blood it also won't tolerate a load of excess glucose in there either. So, your body goes all out to lower the blood glucose levels too, but since the excess glucose can't be metabolized into glycogen...where does it go? Fat stores, I'm afraid.
More: What Does Your Sweat Taste Like?
Got the Munchies?
Only once all the alcohol has been dealt with can your body return to normal and start slowly tapping into those fat stores and replenishing glycogen depleted muscles. The body metabolizes alcohol at roughly 7g-15g of alcohol/hour and a 12-ounce bottle of beer will have somewhere between 10g and 14g of alcohol in there. That means if you have a few beers it could be 3-4 hours before your body can even start to deal with the carbohydrate you consumed in the beer and even longer before it gets around to dealing with that burrito that seemed like such a good idea afterwards.
More: Eat Like a Champion